Another powerful form of evidence is your own first-hand observations.
That’s not to say that you can't accept verbal evidence, but records, data, and first-hand observations are certainly better.
Only data and records can be used to prove a lack of recurrence. - Top management isn't expected to be aware of every corrective action in the organization, but they should be aware of the large ones and overall trends.
Top management awareness would certainly help support a determination of full implementation and communication.
What is the customer's perception of an improvement? Have customers noticed a change in the quality of goods or services?
Broader and more severe problems lead to more profound solutions, which in turn require more evidence to verify effectiveness. The scale of verification must match the scale of the actions taken.If formal training is used, then records of training would be another type of evidence that could be verified. - This is the bottom line: Have the products been improved? Hearsay and verbal affirmations can't be used to prove that products have been improved. - The effectiveness of some corrective action can't be known without ongoing measurement or monitoring of the process.An improved process should ultimately lead to improved products. In these cases, have the controls been set and put in place? Does the data indicate the process has improved and stabilized to the new level?Locate the applicable customers and get their opinions.If customers have not noticed an improvement, it can be logically argued that the actions have not been effective. - If the problem continues to occur at the same level as before, then the corrective action is not effective.